This invention relates to clarifying a contaminated fluid. The contaminant may be a solid, liquid, gel or gas, or any combination of these, and the invention is particularly concerned with the removal of dissolved contaminants. An example would be the separation of vacuum resid (residuum from a vacuum distillation process) from a hydrocarbon oil. The invention also finds application to micron and sub-micron sized contaminants which cannot easily be removed by known separation techniques. "Fluid phase" is used to indicate that the continuous background phase may be either a liquid or gas, liquid being the more usual.